Blind fasteners are commonly used to secure workpieces together when it is otherwise impossible to access the blind side of one of the workpieces. Typically, the workpiece that is accessible by an end-user is referred to as the accessible side workpiece and the workpiece that is inaccessible by an end-user is referred to as the blind side workpiece.
Blind fasteners have wide application in the aerospace industry. In aerospace applications, the blind fastener assembly of the present invention can be used to secure workpieces made of aluminum alloy, other metallic alloys, composites or combinations thereof.
Examples of previously available blind fasteners are disclosed in U.S. Pat. Nos. 4,967,463 and 5,066,179. The principle components of the blind fasteners of FIGS. 1–2 and 9–10 of these patents are a pin, a lock ring, a sleeve and a drive nut. Generally, the pin has the shape of an elongated shank that has a smooth or threaded portion that is adapted to be located within the workpieces to be fastened together and an externally threaded removable pin tail portion. The lock ring, the sleeve and the drive nut are disposed on the pin. The blind fastener assembly is inserted into aligned openings of workpieces that are to be secured together. After installation is complete, the pin, the lock ring and the sleeve would hold the workpieces together.
The pin has an enlarged head at one end of the shank and flats at the opposite end. The flats are wrenching surfaces that allow a tool to rotate the pin during installation of the blind fastener. The pin also has a breakneck groove at a predetermined position on the shank that defines the weakest portion on the shank. When a certain installation load is achieved, the breakneck groove prevents overloading by failing in torsional shear and the removable pin tail portion breaks away from the blind fastener assembly along with the drive nut that is threadedly engaged with the removable pin tail.
The sleeve has a head at one end of the sleeve and the body of the sleeve has a cylindrical shape. The sleeve is not internally threaded and contains a chamfer that is adapted to receive a lock ring. The body of the sleeve has a deformable tail portion that is an integral component of the sleeve and the top of the head may be abraded, coated or knurled.
The drive nut resembles a traditional hexagon nut and is internally threaded. One side of the drive nut may be abraded, coated or knurled as well. The lock ring has a bore and is adapted to be secured within the sleeve chamfer adapted to receive the lock ring.
The assembly process of the previously available blind fastener consists of the lock ring being placed on the pin, followed by the sleeve. The drive nut is then threaded onto the pin until it is seated against the head of the sleeve. The blind fastener assembly is then disposed through aligned openings in a plurality of workpieces. The installation process of the blind fastener is accomplished by use of a tool adapted to hold the drive nut stationary and that also fits over the flats on the pin. The tool prevents the drive nut from rotating, while at the same time rotates the pin. As the pin rotates, the head of the pin is pulled towards the blind side workpiece. The deformable tail portion of the sleeve abuts the outer surface of the blind side workpiece and begins to deform into a bulb by the load placed on the deformable tail portion by the head of the pin. Meanwhile, at the opposite end of the blind fastener assembly, the drive nut is engaging the head of the sleeve. As the pin is screwed tighter and tighter, the head of the sleeve begins to rotate relative to the drive nut. Such a result is undesirable from the standpoint of achieving the maximum grip capacity of the fastener. This undesirable rotation can be reduced by increasing the friction between the drive nut and the head of the sleeve by abrading, coating or knurling that portion of the drive nut and/or the head of the sleeve that is in contact with the drive nut. As can be appreciated, such friction inducing means could damage the head of the sleeve during installation as well. When the deformable tail portion of the sleeve is fully set, the pin stops rotating and the breakneck groove fails causing the removable pin tail to break off with the drive nut that is threadedly engaged with the removable pin tail.
The present invention is more economical than the prior art blind (as Leners of U.S. Pat. Nos. 4,967,463 and 5,066,179 that require use of a lock ring in FIGS. 1–2 and 9–10 because the present invention completely eliminates the use of a lock ring in the blind fastener assembly leading to a savings in the manufacture of the blind fastener assembly and avoiding complexities in function. Also, the present invention has a plurality of dimples on the outer surface of the sleeve body that are disposed thereon by a physical deformation process that places a portion of the sleeve material against the pin shank to prevent loosening of the blind fastener assembly due to vibrations. Additionally, optimum installation performance and reliability are not achieved from the prior art blind fastener because the head of the sleeve can rotate relative to the drive nut. Such rotation would cause abrasion or scraping of the sleeve head. In the embodiments that increase the friction between the drive nut and the sleeve head by abrading, coating or knurling, the friction inducing means could also damage the sleeve head of the blind fastener as well. These results are not only visually apparent, but can also deteriorate the corrosion resistant properties of the sleeve and damage the workpieces under the sleeve head. Also, the drive nut of the prior art can cause large variations in the required installation loads of a particular application due to the potential for rotation of the sleeve relative to the drive nut at high installation loads. That feature can result in a premature break at the breakneck groove and inconsistencies in the amount the deformable tail portion deforms into a bulb. These factors compromise the integrity of the blind fastener.
One solution to the problem of the sleeve rotating relative to the drive nut is through the use of a plurality of non-deformable projections on the drive nut that engage recesses in the sleeve. Such drive nuts have been proposed in U.S. patent application Ser. No. 09/825,711 (WO 02/23055), Ser. No. 09/849,184 and Ser. No. 09/997,500. The instant invention differs from the designs disclosed in these applications due to the integrally formed deformable tail portion of the sleeve that is used to form a bulb. The cited applications all use a separate deformable sleeve that is screwed on the pin. As such, the present invention eliminates the need for a separate deformable sleeve so it is more economical than the design disclosed in the cited patent applications because a component is eliminated.
Additionally, the present invention is a “flush” break blind fastener in substantially all grip ranges of the blind fastener which distinguishes the present invention from the blind fasteners of U.S. Pat. Nos. 4,967,463 and 5,006,179 and U.S. patent application Ser. Nos. 09/825,711, 09/849,184 and 09/997,500 which are not “flush” break blind fasteners in substantially all grip ranges. The term “flush” as used herein means that break off of the removable pin tail is generally at a point flush with the outer surface of the sleeve head or ±0.005 inches above or below that outer surface in substantially all grip ranges for the blind fastener assembly. Break off of the removable pin tail by ±0.005 inches is typically within aerodynamic tolerances and should rarely require a secondary shaving operation to remove the remaining portion of the pin that could project above the outer surface of the sleeve head. Conversely, the substantially flush blind fasteners of U.S. Pat. Nos. 4,967,463 and 5,006,179 and U.S. patent application Ser. Nos. 09/825,711, 09/849,184 and 09/997,500 have a break off point of the removable pin tail at a point generally flush with the sleeve head or slightly above or below that outer surface.
In those grip ranges in the cited patents and patent applications that have the removable pin tail break off at a point slightly above the point that is flush with the outer surface of the sleeve head, the protruding pin that remains must be shaved down by the end-user of the blind fastener assembly to make the pin flush with the outer surface of the sleeve head. Such an operation is costly and time consuming. Additionally, the end-user could damage the sleeve head and/or the accessible side workpiece in the shaving operation. The present blind fastener assembly will not require a shaving application in substantially all grip ranges of the blind fastener.
As can be seen, a need exists in the art for a blind fastener that eliminates the use of lock rings and separate deformable sleeve components in the blind fastener assembly. An additional need exists in the art for a blind fastener that uses a non-destructive drive nut with a plurality of projections that engage recesses in the head of the sleeve that eliminates rotation of the sleeve relative to the drive nut. A further need exists in the art for a flush break blind fastener in substantially all grip ranges for that blind fastener that does not require a subsequent time consuming shaving operation by the end-user of the blind fastener.